This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-231761 filed on Jul. 31, 2000 and Japanese Patent Application No. 2000-231762 filed on Jul. 31, 2000.
1. Field of the Invention
The present invention relates to a geared motor, and more specifically to a geared motor used in a power window system for moving up and down a vehicle door window glass.
2. Description of Related Art
For example, in the power window system for moving up and down the vehicle door window glass or a power sunroof system for moving a vehicle sunroof forward and backward, a geared motor is used as a drive source.
In one previously proposed geared motor, rotational speed of a rotatable shaft of the motor is reduced through a worm and a worm wheel and is outputted from an output shaft that is connected to an end system (e.g., the power window system). The rotatable shaft of the motor is connected to the worm shaft, which is, in turn, meshed with the worm wheel. The worm wheel and the output shaft are rotatably received around a support shaft that is secured to a base of a housing of the motor.
In the previously proposed geared motor, only the one end of the support shaft is secured to the housing (i.e., acting like a cantilever). Thus, relatively large flexure of the support shaft is observed when the output shaft is locked, for example, due to clamping of a foreign object (e.g., human body) between the door window glass of the power window system and a doorframe.
To reduce the flexure of the support shaft when the output shaft is locked, a support hole for supporting the other end of the support shaft is provided in the end system (e.g., the power window system) connected to the geared motor.
However, the previously proposed geared motor and the previously proposed method of supporting the support shaft of the geared motor cannot effectively reduce the flexure of the support shaft by the geared motor alone. Thus, the flexure of the support shaft largely depends on dimensional precision and positional precision of the support hole provided in the end system and also on assembling precision of the geared motor and the end system. As a result, the flexure of the support shaft could exceed a predetermined amount of flexure.
In such a case, appropriate engagement between the worm wheel and the worm cannot be maintained due to the flexure of the support shaft that supports the worm wheel, so that generation of noises in a gear unit and a reduction in durability of the geared motor are likely to occur. In addition, sealing of sliding portion between the support shaft and the output shaft can be deteriorated, so that penetration of water or the like into the housing is allowed, resulting in failure (malfunction) of the geared motor.
Furthermore, in one such previously proposed geared motor, the worm wheel is drivingly connected to a circular disk plate (rotation transmitting portion) of the output shaft through a cushion rubber. The worm wheel is shaped into a generally cylindrical shape and has a base at one end and an opening at the other end. In order to achieve a size reduction, the cushion rubber and the disk plate of the output shaft are received within the cylindrical worm wheel in such a manner that an inner peripheral surface of the worm wheel is slidably engageable with an outer peripheral surface of the disk plate of the output shaft.
Since the inner peripheral surface of the worm wheel slidably engages with the outer peripheral surface of the disk plate of the output shaft, it is possible to restrain radially inward flexure of a cylindrical peripheral wall of the worm wheel by a force radially inwardly exerted from the worm against the worm wheel.
In this geared motor, the worm wheel and the disk plate of the output shaft are normally rotated together through the cushion rubber. However, when the output shaft is locked, the worm wheel is allowed to rotate for a limited angular distance relative to the disk plate of the locked output shaft due to the fact that the cushion rubber is deformed to allow the rotation of the worm wheel for the limited angular distance. This relative rotation restrains application of an excessively large load against the motor when the output shaft is locked. In the previously proposed geared motor, the worm wheel is made of the resin material, and the disk plate is made of a metal material. Since a rigidity of the resin worm wheel is different from the metal disk plate, noises are relatively small (if any) when the worm wheel rotates relative to and slides along the disk plate of the output shaft during the locked state of the output shaft.
In order to reduce a weight of the geared motor, it is conceivable to make the disk plate with a resin material.
However, in the previously proposed geared motor, the inner peripheral surface of the worm wheel makes surface contact with the outer peripheral surface of the disk plate. Thus, if the disk plate of the output shaft is made of the resin material, the rigidity of the worm wheel becomes similar to the rigidity of the disk plate, so that relatively large noises can be generated between the worm wheel and the disk plate when the worm wheel frictionally slides along the disk plate during the locked state of the output shaft.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a geared motor capable of reducing flexure of a support shaft when an output shaft is locked. It is another objective of the present invention to provide a geared motor that is capable of reducing noises generated between a worm wheel and a disk plate of an output shaft when the output shaft is locked.
To achieve the objectives of the present invention, there is provided a geared motor including a housing, a support shaft, an output shaft and a cover. The housing is shaped into a generally cylindrical shape and has a base at one end and an opening at the other end thereof. The housing receives a worm and a worm wheel. The worm is connected to a rotatable shaft of the motor. The worm wheel is meshed with the worm. The support shaft extends along a rotational axis of the worm wheel and has one end secured to the base of the housing and the other end extending out of the housing. The support shaft rotatably supports the worm wheel. The output shaft is rotatably supported about the support shaft and has one end extending out of the housing. The output shaft receives rotation of the worm wheel. The cover is shaped into a disk shape and covers the opening of the housing. The cover includes an output shaft hole, an engaging portion and a shaft support portion. The output shaft hole penetrates through a center of the cover and rotatably receives the output shaft therethrough. The engaging portion is formed along an outer peripheral edge of the cover and is radially supported by the housing. The shaft support portion is slidably engageable with an outer peripheral surface of the output shaft for radially supporting the output shaft.
There is also provided a geared motor including a worm, a worm wheel and an output shaft. The worm is connected to a rotatable shaft of the motor. The worm wheel is meshed with the worm. The worm wheel is shaped into a generally cylindrical shape and has a base at one end and an opening at the other end thereof. The output shaft has a rotation transmitting portion as an integral part thereof. The rotation transmitting portion is coaxially placed within the worm wheel. The worm wheel is allowed to rotate continuously together with the rotation transmitting portion of the output shaft while the output shaft is not locked. The worm wheel is allowed to rotate only for a predetermined angular distance relative to the rotation transmitting portion of the output shaft when the output shaft is locked. An inner peripheral portion of the worm wheel is slidably engageable in line contact with an outer peripheral portion of the rotation transmitting portion of the output shaft.